Year	% of internal resources
1975	32.44604316546763
1976	33.13669064748201
1977	33.827338129496404
1978	34.517985611510795
1979	35.20863309352518
1980	35.89928057553957
1981	36.85791366906474
1982	37.81654676258992
1983	38.77517985611511
1984	39.73381294964028
1985	40.69244604316546
1986	41.23381294964029
1987	39.60575539568346
1988	37.97769784172662
1989	36.34964028776979
1990	34.72158273381295
1991	33.09352517985611
1992	32.74880095926259
1993	32.404076738579136
1994	32.05935251798561
1995	31.714628297392082
1996	31.369904076708632
1997	31.02517985611511
1998	31.506294964028775
1999	31.987410071942445
2000	32.46852517985611
2001	32.19964028776978
2002	31.930755395683452
2003	32.509292565917264
2004	33.087829736241005
2005	33.66636690647481
2006	32.55980215827338
2007	31.45323741007194
2008	31.27697841726619
2009	32.482014388489205
2010	31.48381294964028
2011	31.53776978417266
2012	33.048561151079134
2013	29.09172661870504
2014	29.54946043165468
2015	28.336330935251798
2016	28.076438848920866
2017	27.06294964028777
2018	26.446942446043163
2019	26.272032374100718
2020	26.097122302158272